1. Field of the Invention
The present invention concerns a local coil for acquiring magnetic resonance (MR) data from a shoulder of a patient, an MR apparatus and a method for use of a shoulder coil.
2. Description of the Prior Art
Magnetic resonance tomography (MRT), also called magnetic resonance imaging (MRI), is known e.g. from DE10314215B4.
Modern magnetic resonance systems normally operate with a number of various RF antennas (called coils in the following) for transmission and reception of radio-frequency pulses for exciting nuclei so as to emit magnetic resonance signals and/or for acquisition of the induced magnetic resonance signals. A magnetic resonance system normally has a large whole-body coil (body coil) permanently installed in the magnetic resonance scanner. The whole-body coil is typically arranged cylindrically (for example with a structure known as a birdcage structure) around the patient acquisition chamber in which the patient is supported on a bed (often also called a patient positioning table) during the measurement.
For increasing the signal to noise ratio (SNR) in magnetic resonance imaging, most MRI scanners today use local coils. Local coils are receiving antennas, which are brought close to the region that shall be imaged. For many parts of the body, dedicated coils exist (e.g. shoulder coil, wrist coil, head coil, spine coil, invasive coils e.g. for prostate imaging, etc.). For imaging of a shoulder, today's MRI systems provide a dedicated shoulder coil. Because of economic reasons (cost, scan time, workflow) it is desirable for the local coil to be easily placed on the patient. At the same time, the coil shall be comfortable for the patient. An MRI coil usually consists of a mechanical housing, which houses the antennas (mostly loop or butterfly antennas) and the active electronics which usually consist of a low noise amplifier and tuning/detuning circuits for the antenna.
Conventional shoulder arrays have the shape of a shell e.g. according to FIGS. 2a and 2b. In order to allow the coil to be as close as possible to the imaged volume, different sizes of coils have been built, to account for the different anatomy (shoulder size) of the patient population. Another topic which has to be addressed is the fact that the coil shall be applicable to the left and to the right shoulder. Today this is done by “rotating” the coil 180° along the z-direction (z is parallel to the main magnetic field B0). One disadvantage of today's shoulder array design is the shell-like shape of the coil. This requires that after the patient has been placed on the table, either the patient has to move his/her shoulder into the coil or the coil has to be moved with respect to the patient. This is uncomfortable for the patient, it can be difficult especially for injured patients and is a time consuming step in the workflow. These are the major disadvantages of the shell-design of a shoulder coil.